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POQuestions with different types of answer in NHibernate
 

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    <p>I'm trying to find a tidy solution to a questionnaire problem. Let us say that I have a <code>Questionnaire</code> class which has a collection of <code>Answer</code>s, e.g.</p> <pre><code>public class Questionnaire { public virtual ISet&lt;Answer&gt; Answers {get;set;} } </code></pre> <p>Answers need to be of different types depending on the question, e.g. date of birth, marks out of ten, why do you think etc.</p> <p>My first thought was something like this:</p> <pre><code>public class Question { public virtual QuestionType TypeOfQuestion {get;set;} public virtual string PromptText {get;set;} } public class Answer { public virtual Question Question {get;set;} } public class DateTimeAnswer : Answer { public virtual DateTime Response {get;set;} } public class IntegerAnswer : Answer { public virtual int Response {get;set;} } // etc. </code></pre> <p>The obvious problem would be that from the questionnaire, there is no access to the <code>Response</code> property:</p> <pre><code>questionnaire.Answers[0].Response; // compile error </code></pre> <p>The same would apply to an interface. It would be nicer to use a generic interface, such as:</p> <pre><code>public interface IAnswer&lt;T&gt; { public virtual Question Question {get;set;} public virtual T Response {get;set;} } public class DateTimeAnswer : IAnswer&lt;DateTime&gt; {} </code></pre> <p>The problem then comes in the <code>Questionnaire</code> class, as the type of IAnswer must be supplied:</p> <pre><code>public class Questionnaire { public virtual ISet&lt;IAnswer&lt;???&gt;&gt; Answers {get;set;} } </code></pre> <p>Clearly I don't want to have many collections of IAnswer each with different types. I could use </p> <pre><code>ISet&lt;IAnswer&lt;dynamic&gt;&gt; </code></pre> <p>but then NHibernate wouldn't like it.</p> <p>I realise a compromise is needed somewhere, but I'm not sure which is the prettiest. What would you do?</p>
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